It’s well known that on warm summer days with calm winds, the air in a city can be 2-8 degrees Fahrenheit hotter than the surrounding countryside. Scientists call this phenomenon the ‘urban heat island’ effect.

But now scientists at the UK Met Office think that the effects of global warming will be much more intense in urban areas.

Heat builds up more rapidly in cities because in urban areas, there are fewer trees, and other natural vegetation to shade buildings, block solar radiation and cool the air by evapotranspiration - the evaporation of water from the surfaces of leaves and the soil. In addition, roof and paving materials with low reflectivity absorb more of the sun's rays, causing both surface temperature and overall ambient to build up.

This effect is bad enough for city dwellers but earlier this month the Met Office's Richard Betts told conference listeners in Devon that a doubling of carbon dioxide levels in the atmosphere could triple the intensity of the ‘heat island effect’.

This could mean that cities that now release an average of 20 watts of heat per square metre will in future release 60 watts or more.

"This could have quite significant effects on human health," says Brett.

Other speakers at the Devon conference on Gaia and Climate Change were more forthright about the effects of global warming, saying only a catastrophe will prompt the world to tackle the threat of climate change.

"I do think it will take a disaster to wake us up,” said Professor Lovelock, after the conference. “We had one in Europe last summer with the heatwaves which killed 20,000 people. I'm afraid it will take more of the same, or something else like that, to stir us."

Professor Lovelock, who won acclaim for developing the Gaia Hypothesis, campaigned for new nuclear power sources to be developed and brought into use as the only way that carbon dioxide levels in the atmosphere could be brought down.

"We must stop fretting about the minute statistical risks of cancer from chemicals and radiation,” Lovelock told 50 of Britain's leading climate experts. “Almost a third of us will die from cancer anyway, mainly because we breathe air laden with all that pervasive carcinogen, oxygen. If we fail to concentrate our minds on the real danger, which is global warming, we might die even sooner, as did more than 20,000 unfortunates from overheating in Europe last summer.”

"We have to take global change seriously and immediately and then do our best to lessen the footprint of humans on the Earth," he said.